Twitter cofounder and CEO and Square CEO and founder Jack Dorsey sleeps four to six hours a night

Being at the head of two exciting tech startups doesn't leave too much time for rest. In 2011, Dorsey told Kara Swisher that he was spending eight to 10 hours a day at Square, and eight to 10 hours a day at Twitter.

That left him somewhere around four to six hours a night to sleep, possibly less when travel time is factored in. He still manages to get up at 5:30 every morning to take a jog.

Helena Morrissey, head of personal investing at Legal & General Investment Management, sleeps for five to six hours

Morrissey told The Guardian that she gets up "at 5 in the morning, sometimes earlier," and immediately starts sending emails until her kids get up. She has family dinner scheduled at 7:30 p.m. but works again after that, sometimes for as much as two hours, prepping for the next morning's meetings.

She gets five to six hours of sleep each night and admits to feeling a bit sleep deprived. But that's the job, especially when you've got nine children in addition to running a global investment company.

AOL CEO Tim Armstrong sleeps six hours

Armstrong wakes up around 5 a.m., is out of the house and working from his car by 7 a.m., and works until 7 p.m. He used to start sending emails immediately after waking up, but now restrains himself until 7 a.m.

He says he tries to get six hours of sleep a night, but often ends up operating on less. "It isn't ideal," he told The Guardian.